#[cfg(test)]
mod test {

    fn apply_twicec(f: fn(i32) -> i32, x: i32) -> i32 {
        f(f(x))
    }

    fn square(x: i32) -> i32 {
        x * x
    }

    #[test]
    fn main() {
        let result = apply_twicec(square,3);
        print!("{}",result)
    }
}
